Process control



JuEy 13, 1954 Filed Oct. 1'7, 1949 B. J. MAYLAND PROCESS CONTROL 2Sheets-Sheet l CONTROLLER INVENTOR.

B. J MAYLAND A7" TORNE V 2 Sheets-Sheet 2 INVENTOR- MAYLAND B. J.MAYLAND PROCESS CONTROL GAS July 13, 1954 Filed Oct. 17, 1949 F/G. 3. BYZ ATTORNEYS Patentecl July 13, 1954 PROCESS CONTROL Bertrand J. Mayland,Bartlesville, Okla, assignor to Phillips Petroleum Company, acorporation of Delaware Application October 17, 1949, Serial No. 121,819

4 Claims. 1

This invention relates to process control. In another aspect, it relatesto a novel type of control apparatus.

In carrying out the Fischer-Tropsch synthesis, the synthesis gas isoftentimes manufactured from natural gas and oxygen which are burned ina refractory-lined chamber at temperatures in the range of 2500 to 3000F. and at pressures up to 100 pounds per square inch to produce amixture of carbon monoxide and hydrogen. In carryin out this combustionreaction, the ratio of oxygen to natural gas must be very carefullycontrolled to maintain a proper temperature in the reactor and tominimize formation of undesirable by-products. Heretofore, considerablediificulty has been experienced in properly controlling this combustionreaction in the manner stated and, more particularly, it has beendifficult to properly adjust the ratio of oxygen to natural gas.

It is an object of this invention to provide a novel method of andapparatus for controlling the oxygen to natural gas ratio in themanufacture of synthesis gas for the Fischer-Tropsch reaction.

It is a further object to provide an improved control method for othercommercial processes wherein the amount of feed materials must be verycarefully controlled.

It is a still further object to provide a control device of improvedconstruction for carrying out the aforesaid methods.

Various other objects, advantages and features of the invention willbecome apparent from the following detailed description taken inconjunction with the accompanying drawings, in which:

Figure l is a flow diagram illustrating my novel method and theapparatus for carrying it out, a portion of the control apparatus beingshown in detail;

Figure 2 is a vertical, sectional view of a synthesis gas reactor; and

Figure 3 is a vertical, sectional View of one of the control elements ofFigure 1.

Referring now to Figure 2, a reactor is provided with an inlet conduit Hto which natural gas is admitted through a line 12 and to which air oroxygen is admitted through a line it. In this reactor, which is linedwith refractory material, a temperature of 2500 to 3000 F. is maintainedby partial combustion of the natural gas to form a mixture of carbonmonoxide and hydrogen which is removed through an outlet conduit M. Itwill be understood, of course, that a small amount of carbon dioxide andwater vapor are formed together with the carbon. monoxide and hydrogenand these substances, together with residual methane from the naturalgas, make up the synthesis gas. The tempera ture in the reactor iscontrolled by the amount of oxygen present in the feed stream and, inorder for the reaction to be carried out under equilibrium conditions,the oxygennatural gas mole ratio should be about 0.60 to provide a tem--perature of 2500 F. within the reactor. at this temperature, the amountof residual methane leaving the reactor is negligible and free carbondoes not exist. If the amount of oxygen supplied to the reaction isexcessive, a large amount of carbon dioxide and water vapor are formedwith resultant waste of the oxygen and natural gas admitted to thereactor, and the reactor may be heated to dangerous temperatures. Inaddition, a synthesis gas containing a relatively high proportion ofcarbon dioxide and water vapor is unsuitable for the Fischer-Tropschreaction. In contrast, if the amount of oxygen fed to the reactor is toolow, there is a critical temperature at which excessive amounts of freecarbon appear in the reactor, thus causing a large increase in operatingcost due to the necessity of frequent removal of the free carbon fromthe reactor.

I have discovered that the reactor temperature affords a sensitive andaccurate indication of the presence of excessive oxygen in the feed tothe reactor but that a temperature controller cannot be advantageouslyutilized to determine when the oxygen content of the feed is too low, asthere is no sudden drop in temperature at the point of incipient carbonformation. I have also discovered that the presence of free carbon maybe directly detected to furnish an indication that the oxygen content ofthe feed is too low although, of course, a direct measurement of freecarbon does not provide a basis for control when the oxygen content ofthe feed is excessive. By the joint use of these control features, theoxygen content of the feed is readily adjusted to maintain the criticaltemperature within the reactor at which the production of undesirablebyproducts such as methane, water vapor and carbon dioxide issubstantially decreased while, at the same time, formation of largeamounts of free carbon is prevented. In this connection, it is importantto note that there are two distinct zones within the reactor. These arethe initial combustion zone wherein a high temperature level existswhich is insensitive to changes in the oxygen-natural gas ratio in theiced and the equilibrating zone wherein the equilibrium temperature' ofthe reaction is reached, this latter zone being utilized to provide theupper limit of the oxygen-natural gas ratio control point.

Adjacent the equilibrating zone of the reactor IQ is a photoelectriccell i5 which is focused through a sleeve it upon a closed sleeve 5'! inthe opposite wall of the reactor, the sleeve i'. being provided with acoil it for the circulation of cooling fluid therethrough. The cell 55receives radiation only from the gases within the reactor, as the sleeve[7 is cooled well below the reaction temperature, the radiation fromthese gases in the absence of suspended free carbon, being small andrelatively constant. l-lowevewhen free carbon is suspended in thereactor, it becomes incandescent, thereby producing radiation whichproduces a large increase in the electrical voltage generated by thecell 55. It will be evident, therefore, that the cell is"; is sensitiveto the presence or suspended free carbon in the reactor but it ispractically insensitive to changes in temperature.

The control device further includes a photoelectric cell ES which isfocused through sleeve upon a sheet 2i of a cobalt, chromium, tungstenalloy such as Stellite having a low heat capacity, this sheet beingdisposed in the equilibrating zone of the reactor, and being surround edby a cylindrical shield 22 of similar material to screen out radiationfrom the reactor walls. The shield 22 is, of course, provided with asmall opening 23 to permit radiation to pass through sleeve as to thecell i9. Accordingly, the voltage yond a predetermined value responsiveto the presence of free carbon within the reactor. Photoelectric cell IQis so connected as to actuate control mechanism to reduce theoxygennatural gas ratio when the reactor temperature increases above apredetermined level. manner, optimum reaction conditions are maintainedin the vessel it so as to provide a synthesis gas substantially freefrom methane, and containing only minimum amounts of carbon dioxide andwater vapor, and to prevent deposition of an excessive amount oruncombinedcarbon within the reactor.

The control mechanism referred to is shown in detail by Figure 1 whereinthe parts already described are indicated by like reference characters.Referring now to this figure, it will be noted that photoelectric celli5 is connected through an amplifier 25 to an electronic controller 28which produces a variable air pressure in a conduit 21, this airpressure being proportional to the output voltage produced by the celll5. Similarly, photoelectric cell it is connected through an amplifier28 to an electronic controller 29 which produces a variable air pressurein a conduit 3%, this air pressure being proportional to the outputvoltage of photoelectric cell l9.

The conduit 23' leads to a pressure sensitive element 3i which is shownin detail by Figure 3, from which it will be noted that the air pressureIn this within the inlet conduit is transmitted to a chamber 32 definedby a cylindrical casing 33 and a bellows 34, one end of which isattached to the casing and the other end of which is attached to aflanged portion 35 of a cup-shaped actuating member 3%. Mounted upon themember is a push rod 3'? which extends through a suitable opening in thecasing. A second bellows 3:3 is mounted between the casing and member 35, this bellows having a threaded adjusting nut 39 protruding into theinterior thereof, this nut carrying a block .55 to which is secured oneend or" a spring dl, the other end of this spring being attached to themember 35. It will be apparent that an increase in air pressure inconduit 2'? will cause push rod 3! to move outwardly whereas a decreasein air pressure will cause push rod ill to move inwardly responsive tothe action of spring ll, the sensitivity of the device being governed bythe position or adjusting nut 39. The conduit 39 is attached, in thesame manner, to a similar pressure sensitive device 5 3 having a pushrod i l protruding therefrom.

The push rods 3?, ts are adapted to engage opposite ends of a lever [iswhich is pivoted at 47 to a suitable support. This lever forms a part ofa parallelogram linkage 43 having a movable arm 39 which operates theset pointer assembly M of a conventional controller 5! through lever Itwill be evident that outward movement of push rod 3? will produce amovement of set pointer assembly 5c in one direction whereas outwardmovement of push rod it will move the set pointer assembly in theopposite direction. The amount of set pointer movement per unit movementof lever at is governed by a gear 53 meshing with a gear 5d carrying anadjustable pivoted arm 55 of the parallelogram linkage Q8.

The controller 5! also includes a recording pen 5? which is actuated bya Bourdon tube assembly 58 regulated by a fiowmeter 5G in the oxygensupply conduit it. Thus, the position of pen arm 57 is controlled by therate of flow of oxygen to the reactor 50. The controller 5% alsoincludes a bleed line til which terminates at a nozzle 5! supportedadjacent a bafile plate $2 which is jointly adjustable by the pen armassembly and by the position of set pointer assembly 55. The verticalposition of nozzle Si is controlled by a parallelogram linkage 63 havingsensitivity adjusting gears 56, 65 and which is actuated by a push rod65 of a third pressure sensitive element bl, this element being similarto the one shown by Figure 3. Fluid under pressure is supplied to thepressure sensitive element 51 from a conduit 68 which pressure isadjusted jointly by an automatic control valve 59 regulating the flowofv oxygen through conduit l3 and by a relay valve l'il, this valvehaving. an inner chamber in which is suspended a ball ll. This ballcontrols the proportion of air passing from a supply line to the conduit68 and to the bleed line 66. As is well understood in the art, thenozzle 6!, pen arm assembly 5'5, pressure sensitive element 6?, relayvalve l6, and control valve 59 all cooperate to regulate the flow ofoxygen through the line [3 in such fashion as to make the position ofpen arm 5'! coincide with that of the set pointer.

If the flow of oxygen through line i3 is greater than that determined bythe set pointer, the bailie 52 is moved further from nozzle 6! bymovement of pen arm 5i away from the set pointer, thereby allowing agreater quantity of air to pass through bleed line with the result thatthe pressure in-conduit 58 is reduced and-valve 68 is moved towardclosed position to reduce the flow of oxygen through the conduit l3. incontrast, if the oxygen supply is less than that predetermined by setpointer 51?, baffle 62 moves closer to nozzle s! with the result thatless air passes through bleed line 6% with resultant increase inpressure in conduit 68 which causes opening or" valve 59 to increase theoxygen supply. The pressure sensitive device 61, parallelogram linkage 3and associated parts prevent overshooting of the control. That is, ifthe pen arm 5? is close to the set pointer, a relatively slow adjustmentis made Whereas, if the pen arm is remote from the set pointer, theadjustment is more rapid.

In a preferred embodiment of the invention, a constant fiOW of naturalgas is maintained through conduit 12 by a controller having a flowsensitive device '15 positioned in the conduit and controlling anautomatic valve 11'.

The overall operation of my novel control systern will now be apparentto those skilled in the art. Assuming that natural gas is fed to thereactor from conduit [2 at a constant rataand that oxygen is fed to thereactor through conduit !3 at a rate determined by the setting of valveB9, an excessive temperature in the equilibrating section of the reactorl0 will produce an increased voltage in photoelectric cell I9, which,through the medium of controller 29, produces an increased air pressurein conduit 36 and an outward movement of push arm 44. This movement ofpush arm M is transmitted through lever 16, linkage 4S and lever 52 tothe set pointer assembly causing a rotation thereof in such direction asto decrease the control point on the controller 5!. Thereupon, valve 59is automatically adjusted through cooperation of nozzle 6! baffle 52 soas to reduce the amount of oxygen passing through conduit is until theposition. of pen arm 5? coincides with that of the set pointer. Thedecreased flow of oxygen produces a rapid reduction in the reactortemperature to its optimum value.

In similar manner, formation of uncombined carbon in. an excessiveamount within the reactor iil produces an increased current in thephotoelectric cell !5 which, through the agency of controller 25,produces an increased air pressure in conduit 2'! and an outwardmovement of push arm 3'5. This moves lever 46 in an opposite directionto the motion produced by push arm 5% and causes the control point ofthe unit 5i to be decreased through movement of set pointer assembly bylinkage 48 and lever 52.

Thereupon, the baiile 52 and nozzle 6| cooperate to increase the airpressure in conduit (iii and open valve 69. As a result, the oxygen feedto the reactor is increased with the result that deposition ofuncombined carbon is eliminated. It will be evident, therefore, that Ihave achi ved a major object of my invention in automai' :allyregulating the flow of oxygen to the controller so as to preventexcessive temperatures within the reactor and also to prevent depositionof uncombined carbon. As a result, the synthesis gas passing to theFischer-Tropsch reaction is accurately of a predetermined compositionconsisting essentially of carbon monoxide and hydrogen. ihe applicationof my control method and system to other processes will be evident tothose skilled in the art.

An important feature of my invention resides in the dual controlof theposition of the set further movement of push arm 31.

pointer assembly by the pressure sensitive elements3l and. It will benoted that outward movement of push arm 3'1 moves the set pointer in onedirection through action of linkage is and lever .52. Subsequentmovement of push arm 3? in theopposite direction, however, does notreturn the set pointer to its original position since the lever 46 isnot rigidly connected to the push arm. Accordingly, once lever it ismoved by push arm 31, for example, it stays in position due to theinertia of the linkage system until it is again moved either in areverse direction by outward movement of push arm 45.. or an add tionaldistance in its original direction by a This arrangement, therefore,permits control of a proc ess by two measured variables, in this casetemperature and carbon deposition, without any interference beingestablished in the control system through interaction of the measuredvariables.

Parallelogram linkages 48 and 63, set pointer assembly 50, pressuresensitive element 5'1, and valve '50 are illustrated and explained ininstruments and Process Control by the New York State Vocational andPractical Arts Association, Delmar Publishers, Inc, Albany, N. L, 1945,pages 4041, 54-59 and 134-139, and in U. S. Patent 2,361,885 (1944),Tate et a1.

While the invention has been described. in connection with a present,preferred embodiment thereof, it is to be understood that thisdescription is illustrative only and is not intended to limit theinvention, the scope of which is defined by the appended claims.

I claim:

1. Apparatus for controlling a reaction wherein a synthesis gasconsisting essentially of carbon monoxide and hydrogen is formed by thepartial combustion of methane in oxygen which comprises, in combination,a reactor having inlet and outlet conduits, a photoelectric cell focusedupon a-surface in'said reactor, 2. second photoelectric cell, an openingin said reactor opposite said second photoelectric cell, means forfocusing sa' 1 control valve'in said line, a controller for ope. atingsaid'valve, means for feeding the output of said first cell to saidcontroller to close said valve when the photoelectric current risesabove a predetermined value, and means for feeding the output of saidsecond photoelectric cell to said controller to open said valve when thephotoelectric current rises above a predetermined value.

2. Apparatus for controlling a reaction wherein a synthesis gasconsisting essentially of carbon monoxide and hydrogen is formed by thepartial combustion of methane in oxygen which comprises, in combination,a reactor having inlet and outlet conduits, a photoelectric cell focusedupon a surface in said reactor, a second photoelectric cell, an openingin said reactor opposite said second photoelectric cell, means forfocusing said photoelectric cell on said opening, a pair of voltageamplifiers, a pair of electronic controllers actuated, respectively, bysaid amplifiers, means for feeding the output of said photoelectriccells to the respective amplifiers, a line for supplying oxygen to saidinlet conduit, an automatic control valve in said line, a pneumaticcontroller for operating said valve, an air line connecting one of saidelectronic controllers to said pneumatic controller to close said valvewhen the photoelectric current in said first cell rises above apredetermined value, an air line connecting said second electroniccontroller to said pneumatic controller to open said valve when thephotoelectric current in said second cell rises above a predeterminedvalue, a line for supplying methane to said inlet conduit. and acontroller for maintaining a constant rate of flow in said methane line.

3. Apparatus for controlling a reaction wherein a synthesis gasconsisting essentially of carbon monoxide and hydrogen is formed by thepartial combustion of methane in oxygen which comprises, in combination,a reactor having inlet and outlet conduits, a photoelectric cell focusedupon a. surface in said reactor, a second photoelectric cell, an openingin said reactor opposite said second photoelectric cell, means forfocusing said photoelectric cell on said opening, a pair of voltageamplifiers, a pair of electronic controllers actuated, respectively, bysaid amplifiers, means for feeding the output of said photoelectriccells to the respective amplifiers, a line for supplying oxygen to saidinlet con duit, an automatic control valve in said line, a pneumaticcontroller for operating said valve, said pneumatic controller includinga movable pen arm assembly for recording the oxygen flow rate in saidline and for controlling said valve together with a set pointer fordetermining the control point of said pen arm, a linkage for actuatingsaid set pointer including a pivoted lever, a bellows at each end ofsaid lever, a push arm on each bellows which is engagable with theadjacent end of said lever, and a pair of air lines for connecting therespective electronic controllers to said bellows.

4. An apparatus for controlling the hydrogen and carbon monoxidecontents of synthesis gas produced in a process in which a hydrocarbongas is reacted with oxygen to produce said synthesis gas, said apparatuscomprising in combination: a reactor; means for supplying hydrocarbongas to said reactor; an oxygen inlet to said reactor; an efiluent lineattached to said reactor; a control valve in said oxygen inlet; a closedtube attached to said reactor adjacent an initial combustion zonetherein and adapted to be maintained at a temperature lower than that ofthe interior of said reactor; a refractory member positioned in anequilibrating zone in said reactor; a photoelectric cell adapted to befocused on the interior of said closed tube; another photoelectric celladapted to be focused on said refractory member; means responsive to thevoltage output of said first-mentioned photoelectric cell and adapted toopen said control valve when the voltage output of said first-mentionedphotoelectric cell exceeds a predetermined amount responsive to thepresence of incandescent carbon in said initial combustion zone; andmeans responsive to the voltage output of said second-mentionedphotoelectric cell and adapted to throttle said control valve when thevoltage output of said second-mentioned photoelectric cell exceeds apredetermined amount responsive to the radiation of said refractory mmber.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,156,412 Lincoln Oct. 12, 1915 1,258,345 Lincoln Mar. 5, 19181,305,227 Lincoln May 27, 1919 1,728,929 Ernst et a1 Sept. 24, 19291,923,865 Handforth Aug. 22, 1933 1,960,912 Larson May 29, 19341,962,676 Albright June 12, 1934: 2,081,170 Dreffein May 25, 19372,171,596 Parker Sept. 5, 1939 2,310,298 Kuhl et a1. Feb. 9, 194:32,361,885 Tate et a1 Oct. 31, 1944 2,375,820 Ridings et a1 May 15, 19452,393,950 Allen Feb. 5, 1946 2,483,132 Gaucher Sept. 27, 1919 2,562,507Pierce -1 July 31, 1951 FOREIGN PATENTS N umber Country Date 711,586France Sept. 12, 1931 300,328 Great Britain Nov. 15, 1928 OTHERREFERENCES Industrial and Engineering Chemistry, Sept.

1945, pages 816-820.

Chemical and Metallurgical Engineering, May 1943, pages 108 to 125.

1. APPARATUS FOR CONTROLLING A REACTION WHEREIN A SYNTHESIS GASCONSISTING ESSENTIALLY OF CARBON MONOXIDE AND HYDROGEN IS FORMED BY THEPARTIAL COMBUSTION OF METHANE IN OXYGEN WHICH COMPRISES, IN COMBINATION,A REACTOR HAVING INLET AND OUTLET CONDUITS, A PHOTOELECTRIC CELL FOCUSEDUPON A SURFACE IN SAID REACTOR, A SECOND PHOTOELECTRIC CELL, AN OPENINGIN SAID REACTOR OPPOSITE SAID SECOND PHOTOELECTRIC CELL, MEANS FORFOCUSING SAID SECOND CELL UPON SAID OPENING, A LINE FOR SUPPLYING OXYGENTO SAID INLET CONDUIT, AN AUTOMATIC CONTROL VALVE IN SAID LINE, ACONTROLLER FOR OPERATING SAID VALVE, MEANS FOR FEEDING THE OUTPUT OFSAID FIRST CELL TO SAID CONTROLLER TO CLOSE SAID VALVE WHEN THEPHOTOELECTRIC CURRENT RISES ABOVE A PREDETERMINED VALUE, AND MEANS FORFEEDING THE OUTPUT OF SAID SECOND PHOTOELECTRIC CELL TO SAID CONTROLLERTO OPEN SAID VALVE WHEN THE PHOTOELECTRIC CURRENT RISES ABOVE APREDETERMINED VALUE.